1. Field of the Invention
The invention relates to a seat belt device, and more particularly to a seat belt device which can tighten seat belt webbing in the event of an emergency.
2. Related Art
A seat belt device of an automobile has an Emergency Locking Retractor (ELR) which locks seat belt webbing so as not to be unwound from a retractor when an acceleration exceeding a predetermined threshold is exerted on the automobile. In addition, some retractors have a pretensioner and a load limiter.
The pretensioner described above can immediately wind the seat belt webbing at an earlier time of impact exerted on the automobile, restraining an occupant from moving forward. The load limiter has Energy Absorption (EA), absorbing the kinetic energy of the occupant due to his or her inertial movement with the seat belt webbing. Various kinds of seat belt devices have been proposed, which can control the pretensioner and the load limiter to decrease the restrictive feeling of the restrained occupant, while maintaining safety.
A seat belt device has been invented, which can control a conventional lock mechanism to work normally in the event a pyrotechnic pretensioner is activated (see Japanese Unexamined Patent Application Publication No. 2002-326558). Another seat belt device has been invented, which can stably control a load limiter when a pyrotechnic pretensioner operates (see Japanese Unexamined Patent Application Publication No. 2003-191819).
The seat belt devices disclosed in Japanese Unexamined Patent Application Publication Nos. 2002-326558 and 2003-191819 block the transmission of a rotation from a motor pretensioner to a spindle when a pyrotechnic pretensioner operates. However, these seat belt devices require a new mechanism including additional parts (a solenoid for example) and components in order to block the transmission of power from the motor. Furthermore, since it is necessary to place the mechanism in a vacant space adjacent to the existing motor and pyrotechnic pretensioners, the assembly of the seat belt device becomes complicated, which may result in increased cost. Therefore, it may be preferable that the seat belt device is compatible with the existing pretensioners.
In a conventional seat belt device of an automobile, for example, an occupant moving forward unwinds seat belt webbing after a pyrotechnic pretensioner has been activated. In other words, a spindle onto which the seat belt webbing is wound rotates in a direction to unwind the seat belt webbing. In contrast, when a motor pretensioner works after the pyrotechnic pretensioner has been activated, it may occur that the spindle rotates in a direction to wind the seat belt webbing. This is due to the fact that a clutch mechanism to restrict a reverse rotation of the motor may engage with the spindle while the motor is rotating in a direction to wind the seat belt webbing. If such a phenomenon occurs, the seat belt device can not perform appropriate Energy Absorption (EA). In addition, the seat belt device has a drawback that the load imposed on the motor pretensioner is excessive. The present invention has been provided to solve such a drawback.